A bunch of us fly Beavers with the 2015/4100 motor. We use the stock gearing and prop, C gear, 10-8 prop.
Most of the time we use 2s packs, altough if it's windy we use 2 packs in parallel for more weight, or 3s packs.
The Beaver is not really strong enough for the 3s, so throttle management is key.
In any case use the strapping tape on the wings in the X pattern. Without it they will flutter.
Pin the struts and glue them very well to the fuse and wing. Use a larger piece of foam or thin plywood to glue the clevises to, and check them often before flying. I've seen a lot of them let go. Light foam wheels around 2.5" diameter are great. The stock wheels don't last long. MPI makes some nice spoked ones.
An improvement is to make a steerable tail wheel. Really helps with ground handling, since the Beaver always want to ground loop. I took a new wire and poked it up through the hole where the old one was, then bent and taped it to the rudder. I ran the wire through a small tube, like inner nyrod, to keep it from wearing on the foam.